Voyager 1 Approaches Boundary of Interstellar Space

The 34-year-old probe is detecting a sharp increase in the intensity of cosmic rays, a sign that it's close to becoming the first man-made object to travel beyond the Solar System.

Humankind's first foray into interstellar space may be upon us as NASA's Voyager 1 spacecraft travels through a region in space that scientists believe marks the border between our solar system and the vast reaches between stars, the space agency reported this week.

"The laws of physics say that someday Voyager will become the first human-made object to enter interstellar space, but we still do not know exactly when that someday will be," Ed Stone, Voyager project scientist at the California Institute of Technology in Pasadena, said in a statement. "The latest data indicate that we are clearly in a new region where things are changing more quickly. It is very exciting. We are approaching the solar system's frontier."

Voyager 1, launched in 1977 to explore the outer solar system and beyond, is now sending signals to Earth from 11.1 billion miles away, far beyond the orbits of Neptune and the dwarf planet Pluto, that indicate a marked increase in the intensity of charged particles originating from outside the heliosphere.

That could indicate that the venerable space probe has passed or is passing out of the heliosheath, the outermost layer of the comet-shaped "bubble" surrounding our Sun that is thinnest in the direction of our star's path through space (see artist's concept below). The intensity of energetic charged subatomic particles, or cosmic rays, should rise significantly as Voyager 1 ventures past the furthest reaches of the solar wind and that is what the data the probe is sending back suggests is happening.

Previous estimates have suggested that it will be another two years or more before Voyager 1 arrives at the heliopause, in theory the boundary where the interstellar medium and the solar wind fight to a draw and truly outer space begins.

Stone said the probe's pair of High Energy telescopes detected "a gradual increase of about 25 percent in the amount of galactic cosmic rays Voyager was encountering" from January 2009 to January 2012. But the rate of increase is escalating fast, he said.

"More recently, we have seen very rapid escalation in that part of the energy spectrum. Beginning on May 7, the cosmic ray hits have increased five percent in a week and nine percent in a month," Stone said.

An increase in cosmic rays is just one measure that scientists will use to determine when Voyager I has passed into interstellar space. Another is the intensity of particles generated by the Sun and blown around the heliosphere by the solar wind.

So far, the probe has detected a decline in those particles in the region of space it's traveling through, but Voyager scientists said the drop has not been precipitous enough to make the call that the spacecraft has officially traveled beyond the Solar System.

Voyager 1 also measures the direction of the magnetic field lines surrounding the spacecraft, which will help to determine when it has arrived in interstellar space.

"While Voyager is still within the heliosphere, these field lines run east-west. When it passes into interstellar space, the team expects Voyager will find that the magnetic field lines orient in a more north-south direction. Such analysis will take weeks, and the Voyager team is currently crunching the numbers of its latest data set," NASA said.

Voyager 2, also launched in 1977, is currently more than 9.1 billion miles from the Sun and set to become the second man-made object to travel beyond the Solar System. Both probes are in good working order 34 years after being shot into the heavens.

"When the Voyagers launched in 1977, the space age was all of 20 years old," said Stone. "Many of us on the team dreamed of reaching interstellar space, but we really had no way of knowing how long a journey it would be or if these two vehicles that we invested so much time and energy in would operate long enough to reach it."

Damon Poeter got his start in journalism working for the English-language daily newspaper The Nation in Bangkok, Thailand. He covered everything from local news to sports and entertainment before settling on technology in the mid-2000s. Prior to joining PCMag, Damon worked at CRN and the Gilroy Dispatch. He has also written for the San Francisco Chronicle and Japan Times, among other newspapers and periodicals.
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